Lens barrel

ABSTRACT

A lens barrel includes a ring member having a cam groove formed on an inner peripheral surface thereof; a lens support ring positioned in the ring member and supported thereby to be rotatable with respect to the ring member, the lens support ring having a first cam follower which is engaged in the cam groove of the ring member; a biasing ring coupled to the lens support ring to be movable in an optical axis direction and to be non-rotatable with respect to the lens support ring, the biasing ring having a second cam follower which is engaged in the cam groove of the ring member; and a biasing device for biasing the lens support ring and the biasing ring in opposite directions to press the first and second cam followers against opposite guide surfaces of the cam groove.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens barrel which incorporates aguide mechanism using a cam groove(s) and a cam follower(s) which arerespectively engaged in the cam groove(s).

2. Description of the Related Art

In a lens barrel which incorporates a guide mechanism using at least onecam groove and at least one cam follower which is engaged in the camgroove to move one or more elements of the lens barrel in apredetermined moving manner, there are various known methods of removingbacklash and play between the cam follower and the cam groove to ensurea high positioning accuracy of one or more lens groups of the lensbarrel. According to a simple method of removing such backlash and play,only a minimum clearance is established with a high degree of precisionbetween each cam groove and the associated cam follower so that suchbacklash and play does not have to be taken into account. However, it isnot practical to form the cam follower and the cam groove with such ahigh degree of precision in terms of the production cost, and also intime and effort.

If each cam groove extends in a direction inclined with respect to boththe optical axis, of the lens system provided in the lens barrel, and acircumferential direction of the lens barrel, each cam groove can beconsidered to control forward and reverse rotations of either a followermember on which the cam follower is formed or a corresponding cam memberon which the cam groove is appropriately formed in a manner so that eachcam follower remains in contact with one of the opposite guide surfaces(guide surfaces) of the associated cam groove, between which the camfollower is positioned, for the purpose of guiding each cam followeralong the associated cam groove with a high degree of precision.However, this method is not effective in removing backlash and playbetween the cam follower and specific portions of the cam groove whichdo not extend in a direction inclined with respect to both the opticalaxis of the lens system and a circumferential direction of the cammember, i.e., which extends only in a circumferential direction of thecam member, perpendicular to the optical axis.

In another method of removing backlash and play between the cam followerand the cam groove, a device for removing such backlash and play usingone or more spring members as a biasing device is known in the art.However, it has formerly been difficult to simplify and miniaturize thestructure of this conventional device. For instance, although the lensbarrel needs to be provided around the aforementioned biasing devicewith a reaction force receiving portion (or portions) which receives thereaction force of the biasing device, the reaction force receivingportion tends to become a leading cause of an increase in size of thelens barrel because the reaction force receiving portion is designed asan independent member in conventional lens barrels. In addition, in sucha conventional backlash and play removing device, a constant biasingforce is applied between the cam groove and the cam follower regardlessof whether the lens barrel is in use. Due to this structure, a largefriction is produced between each cam groove and the associated camfollower even when backlash and play between the cam follower and thecam groove do not have to be reduced to a minimum, e.g., during the timethe lens barrel changes its position from an accommodation position to aready-to-photograph position in a zooming range (e.g., a wide-angleextremity) if the lens barrel is a zoom lens barrel. Such a largefriction becomes an unfavorable resistance to the engagement between thecam follower and specific portions of the cam groove.

As another problem, if each cam follower bumps hard against one of theopposite guide surfaces of the associated cam groove due to anaccidental impact (external force) on the lens barrel, a portion of eachcam groove against which the associated cam follower bumps hard isdamaged, thus making it impossible for the damaged cam groove to guidethe associated cam follower smoothly afterwards.

SUMMARY OF THE INVENTION

The present invention provides a lens barrel which incorporates a guidemechanism using at least one cam groove and at least one cam followerwhich is engaged in the cam groove, wherein backlash and play betweenthe cam groove and the cam follower can reliably be removed with asimple and small mechanism.

For example, a lens barrel including a ring member having a cam grooveformed on an inner peripheral surface thereof, the cam groove includingopposite guide surfaces; a lens support ring positioned in the ringmember and supported thereby to be rotatable with respect to the ringmember, the lens support ring having a first cam follower which isengaged in the cam groove of the ring member; a biasing ring coupled tothe lens support ring to be movable in an optical axis direction and tobe non-rotatable about the optical axis with respect to the lens supportring, the biasing ring having a second cam follower which is engaged inthe cam groove of the ring member; and a biasing device for biasing thelens support ring and the biasing ring in opposite directions in theoptical axis direction to press the first cam follower and the secondcam follower against the opposite guide surfaces of the cam groove.

It is desirable for the biasing device to bias the lens support ring andthe biasing ring in opposite directions away from each other in theoptical axis direction.

It is desirable for the opposite guide surfaces of the cam groove toinclude a front guide surface and a rear guide surface, the front guidesurface being provided at a forward position of the optical axis and therear guide surface being provided at a rearward position of the opticalaxis. The first cam follower is pressed against the front guide surfaceand the second cam follower is pressed against the rear guide surface.

It is desirable for the first cam follower to be formed on an outerperipheral surface of the lens support ring, at a rear end thereof inthe optical axis direction. A radial end portion of the first camfollower is engaged in the cam groove, and a base portion of the firstcam follower is fitted in a recess formed on the biasing ring.

It is desirable for the first cam follower and the second cam followerto be pressed against one of the opposite guide surfaces and the otherof the opposite guide surfaces, respectively, with the first camfollower and the second cam follower not being in contact with the otherof the opposite guide surfaces and the one of the opposite guidesurfaces, respectively.

It is desirable for a mutual distance in the optical axis directionbetween the first cam follower and the second cam follower to change inaccordance with movement of the first and second cam followers along thecam groove.

The lens barrel can include a zoom lens barrel. It is desirable for thecam groove to include a zooming groove portion used to change a positionof the zoom lens barrel between a telephoto extremity and a wide-angleextremity, and a photographing preparation groove portion which extendsfrom one end of the zooming groove portion to an accommodation position.The mutual distance between the first and second cam followers when thefirst and second cam followers are engaged in thephotographing-preparation groove portion is greater than when the firstand second cam followers are engaged in the zooming groove portion.

It is desirable for the zooming groove portion to extend only in acircumferential direction of the lens support ring, perpendicular to theoptical axis. It is desirable for the photographing-preparation grooveportion extends in a direction inclined with respect to both the opticalaxis and the circumferential direction of the lens support ring. Thefirst cam follower and the second cam follower are engaged in the camgroove at different circumferential positions of the lens support ring.

The ring member includes a stationary barrel fixed to a camera body, thelens barrel further including a rotation transfer ring via which arotational motion is transferred to the lens support ring, the rotationtransfer ring being supported by the ring member so as to be immovablein the optical axis direction and to be rotatable about the optical axiswith respect to the ring member.

It is desirable for the rotation transfer ring to be engaged with thelens support ring and the biasing ring to be non-rotatable with respectto both the lens support ring and the biasing ring.

The biasing device can include at least one compression spring providedbetween the lens support ring and the biasing ring.

The lens barrel can further include a motor which generates therotational motion, so that the rotation transfer ring transfers therotational motion from the motor to the lens support ring.

The lens support ring can include a plurality of first cam grooves and aplurality of second cam grooves which are formed on an inner peripheralsurface of the lens support ring and an outer peripheral surface of thelens support ring, respectively.

The present disclosure relates to subject matter contained in JapanesePatent Application No.2001-335565 (filed on Oct. 31, 2001) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is an exploded perspective view of an embodiment of a zoom lensbarrel according to the present invention;

FIG. 2 is an exploded perspective view of a portion of the zoom lensbarrel shown in FIG. 1;

FIG. 3 is an exploded perspective view of another portion of the zoomlens barrel shown in FIG. 1;

FIG. 4 is a perspective view of a second lens group moving frame and ashutter unit fixed to the second lens group moving frame, which areshown in FIG. 1, as viewed obliquely from front of the second lens groupmoving frame;

FIG. 5 is a perspective view of the second lens group moving frame andthe shutter unit fixed to the second lens group moving frame, which areshown in FIG. 1, as viewed obliquely from rear of the second lens groupmoving frame;

FIG. 6 is a view similar to that of FIG. 4, showing a position where thesecond lens group moving frame has rotated by a predetermined amount ofrotation with respect to the shutter unit from the position shown inFIG. 4;

FIG. 7 is a view similar to that of FIG. 5, showing a position where thesecond lens group moving frame has rotated by a predetermined amount ofrotation with respect to the shutter unit from the position shown inFIG. 5;

FIG. 8 is an axial cross sectional view of the zoom lens barrel shown inFIG. 1, above the optical axis, showing the zoom lens barrel in anaccommodation position;

FIG. 9 is a view similar to that of FIG. 8, showing the zoom lens barrelin a wide-angle position;

FIG. 10 is a view similar to that of FIG. 8, showing the zoom lensbarrel in a telephoto position;

FIG. 11A is an enlarged perspective view of the cam ring;

FIG. 11B is an enlarged perspective view of a rotational ring shown inFIG. 1;

FIG. 12 is a perspective view of the cam ring, the rotational ring and abiasing ring fitted on the rear end of the cam ring in the accommodationposition shown in FIG. 8;

FIG. 13 is a view similar to that of FIG. 12, showing the cam ring,rotational ring and the biasing ring in a photographing position;

FIG. 14 is a cross sectional view of the cam ring, the rotational ringand the biasing ring;

FIG. 15 is a perspective cross sectional view of the cam ring, therotational ring and the biasing ring;

FIG. 16 is a developed view of an outer peripheral surface of the camring;

FIG. 17A is a developed view of outer peripheral surfaces of the camring and the biasing ring fitted on the rear end of the cam ring;

FIG. 17B is a developed view of an outer peripheral surface of therotational ring;

FIG. 18 is a developed view of outer peripheral surfaces of the camring, the rotational ring and the biasing ring in the accommodationposition shown in FIG. 12;

FIG. 19 is a developed view of outer peripheral surfaces of the camring, the rotational ring and the biasing ring in the photographingposition shown in FIG. 13;

FIG. 20 is a developed view of an inner peripheral surface of the camring;

FIGS. 21A through 21J are developed perspective diagrams of the camring, a first lens group moving frame and the second lens group movingframe which are associated with one another, showing their positionalrelationships, step by step, in the case where the cam ring rotates fromthe accommodation position to the wide-angle extremity;

FIG. 22 is a graph showing variations in angle of rotation of the secondlens group moving frame with respect to the cam ring;

FIG. 23 is a graph showing the relationship among the angle of rotationof the cam ring and the axial positions of the first and second lensgroup moving frames, wherein their respective accommodation positionsare represented by the point of origin (zero) of the graph;

FIG. 24 is a perspective view of the first lens group moving frame andthe second lens group moving frame fitted in the first lens group movingframe in the accommodation position shown in FIG. 8;

FIG. 25 is a view similar to that of FIG. 24, showing a state wherethree linear guide keys of the second lens group moving frame andcorresponding three linear guide grooves of four linear guide grooves ofthe first lens group moving frame are aligned in the optical axisdirection of the zoom lens barrel so that the three linear guide keyscan be engaged in the corresponding three linear guide keys,respectively;

FIG. 26 is a front elevational view of the first lens group moving frameand the second lens group moving frame fitted in the first lens groupmoving frame in the accommodation position shown in FIG. 8;

FIG. 27 is a view similar to that of FIG. 26, showing a state where thethree linear guide keys of the second lens group moving frame and thecorresponding three linear guide grooves of the four linear guidegrooves of the first lens group moving frame are aligned in the opticalaxis direction of the zoom lens barrel so that the three linear guidekeys can be engaged in the corresponding three linear guide keys,respectively; and

FIG. 28 is a developed view of an inner peripheral surface of astationary barrel shown in FIG. 1.

FIG. 29 shows an enlarged portion of the developed view of FIG. 28.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The illustrated embodiment of a zoom lens barrel, an explodedperspective view of which is shown in FIG. 1, is a telescoping zoom lensbarrel of a digital camera.

As can be clearly seen in FIGS. 8 through 10, the zoom lens barrel 10 isprovided with a photographing optical system constructed of three lensgroups: a first lens group L1, a second lens group L2, and a third lensgroup L3, in that order from the object side (the left side as viewed inFIGS. 8 through 10). The first and second lens groups L1 and L2 aredriven to move along an optical axis O relative to the third lens groupL3 while varying the distance therebetween to perform a zoomingoperation. The third lens group L3 serves as a focusing lens group, andis driven to move along the optical axis O to perform a focusingoperation.

As shown in FIG. 1, the zoom lens barrel 10 is provided with astationary barrel (ring member) 11, a shaft holding member 12, a CCDholding frame 13, a low-pass filter 14, a rectangular sealing member 15,a CCD 16 and a CCD pressure plate 17, which are all stationary membersfixed to a camera body (not shown). Namely, none of these elementseither move along an optical axis O (see FIGS. 8, 9 and 10) nor rotateabout the optical axis O. The stationary barrel 11 is fixed to thecamera body by set screws. As shown in FIGS. 1 and 3, the stationarybarrel 11 is provided with an outer cylindrical portion 11 b and agutter-shaped gear holding portion 11 c. Three cam grooves 11 a areformed on an inner peripheral surface of the outer cylindrical portion11 b at equi-angular intervals (intervals of 120 degrees) in acircumferential direction of the stationary barrel 11. The outercylindrical portion 11 b is further provided on the inner peripheralsurface thereof with three linear guide grooves 11 d extending parallelto the optical axis O. Three linear guide keys 27 a formed on a secondring (outer ring) 27 are respectively engaged in the three linear guidegrooves lid. The zoom lens barrel 10 is provided with a vertical motor18 having a rotating shaft extending in a vertical direction of thecamera (the vertical direction as viewed in FIG. 1). A drive gear 19 aof a reduction gear train 19 engaged with the rotating shaft of thevertical motor 18 is mounted on the gear holding portion 11 c to partlyproject into the inside of the stationary barrel 11 through a throughhole (not shown) on an upper surface of the stationary barrel 11.

The low-pass filter 14, the sealing member 15 and the CCD 16 are fixedto the rear face of the CCD holding frame 13 with the CCD pressure plate17.

The zoom lens barrel 10 is provided with a rotational ring (rotationtransfer ring) 20 on which a circumferential gear portion 20 a meshingwith the drive gear 19 a is formed. The rotational ring 20 is positionedin the rear of the stationary barrel 11 to be freely rotatable about theoptical axis O without moving in the direction of the optical axis O(i.e., in the optical axis direction) with respect to the stationarybarrel 11. Three rotation-transmission arms 20 b project forwards fromthe rotational ring 20 at equi-angular intervals (intervals of 120degrees) in a circumferential direction of the rotational ring 20. Eachof the three rotation-transmission arms 20 b is provided on an innersurface thereof with a rotation-transmission groove 20 c extendingparallel to the optical axis O.

The zoom lens barrel 10 is provided in the stationary barrel 11 with acam ring (lens support ring) 22 positioned in front of the rotationalring 20. As shown in FIG. 11A, the cam ring 22 is provided, on an outerperipheral surface thereof in the rear end of the cam ring 22, withthree bottomed engaging recesses 22 a shaped to substantially correspondto the three rotation-transmission arms 20 b. The rear end of eachengaging recess 22 a is formed as an open end. The radial depth of eachengaging recess 22 a is substantially the same as the radial thicknessof each rotation-transmission arm 20 b. The cam ring 22 is provided inthe vicinity of the rear end thereof with an annular wall (outer flange)23 projecting radially outwards from the cam ring 22. The cam ring 22 isprovided on a front surface of the annular wall 23 with three bayonetprongs 24 each being elongated in a circumferential direction of the camring 22 and having an L-shaped cross section. The cam ring 22 isprovided, between an inner surface of the annular wall 23 and the threeengaging recesses 22 a and between the three bayonet prongs 24 and theset of engaging recesses 22 a, with three slots S (see FIG. 14)penetrating therethrough in the optical axis direction so that the threerotation-transmission arms 20 b are held between radial-bottom surfacesof the three engaging recesses 22 a and the respective inner surfaces ofthe annular wall 23 in the three slots S to be movable in the opticalaxis direction with respect to the cam ring 22, respectively. Each slotS has an arc shape which extends in a circumferential direction asviewed from the front (or rear) of the zoom lens barrel 10. The cam ring22 is provided in the three engaging recesses 22 a with three guide keys22 b which extend in the optical axis direction to be slidably engagedwith the three rotation-transmission grooves 20 c, respectively. The camring 22 is provided, on an outer peripheral surface thereof atequi-angular intervals (intervals of 120 degrees) in a circumferentialdirection of the cam ring 22, with three follower pins (first camfollowers) 22 f which extend radially outwards to be engaged in thethree cam grooves 11 a of the stationary barrel 11, respectively. Thefront-end portion of the guide key 22 b is positioned in the slot S.

The three rotation-transmission arms 20 b of the rotational ring 20 areslidably engaged in the three engaging recesses 22 a to be freelymovable in the optical axis direction with respect to the cam ring 22with the three guide keys 22 b being engaged in the threerotation-transmission grooves 20 c, respectively. The threerotation-transmission arms 20 b are respectively prevented from comingoff the three engaging recesses 22 a radially outwards by the annularwall 23, which is positioned radially outside the three engagingrecesses 22 a.

As shown in FIG. 3, the zoom lens barrel 10 is provided with a biasingring 21 which is fitted on the rear end of the cam ring 22 to bepositioned behind the annular wall 23. The biasing ring 21 is providedon an inner peripheral surface thereof with three recesses 21 a in whichthe three rotation-transmission arms 20 b are respectively inserted tobe freely slidable in the optical axis direction. The biasing ring 21 isprovided, on an outer peripheral surface thereof at equi-angularintervals (intervals of 120 degrees) in a circumferential direction ofthe biasing ring 21, with three recesses 21 b. The biasing ring 21 isfurther provided, on an outer peripheral surface thereof at equi-angularintervals (intervals of 120 degrees) in a circumferential direction ofthe biasing ring 21, with three follower pins 21 f in the close vicinityof the three recesses 21 b, respectively. The three follower pins 22 fof the cam ring 22 are engaged in the three recesses 21 b.

The biasing ring 21 is provided, on a front surface thereof atequi-angular intervals (intervals of 120 degrees) in a circumferentialdirection of the biasing ring 21, with three spring-support projections21 c, and the cam ring 22 is provided in the rear thereof with threespring-support recesses (not shown) formed to correspond to the threespring-support projections 21 c. One end of each of the threecompression helical springs 26 are inserted into the threespring-support recesses while the other ends thereof are fitted on thethree spring-support projections 21 c so that the three compressionhelical springs 26 are held under compression between the threespring-support recesses and the biasing ring 21. Accordingly, the camring 22 is always biased toward the front of the optical axis direction,while the biasing ring 21 is biased toward the rear of the optical axisdirection. Namely, the cam ring 22 and the biasing ring 21 are biased inopposite directions away from each other along the optical axis O by thethree compression helical springs 26.

As shown in FIG. 28, the three follower pins 21 f of the biasing ring 21and the three follower pins 22 f of the cam ring 22 are engaged in thethree cam grooves 11 a of the stationary barrel 11 at differentcircumferential positions, respectively. Each cam groove 11 a includes alinear groove portion 11 a 1, an accommodation groove portion 11 a 2, aposition-changing groove portion (photographing preparation grooveportion) 11 a 3 and a zooming groove portion 11 a 4. The linear grooveportion 11 a 1 extends in the optical axis direction. The accommodationgroove portion 11 a 2 extends in a circumferential direction of the camring 22. The position-changing groove portion 11 a 3 extends in adirection inclined with respect to both the optical axis O and acircumferential direction of the cam ring 22. The zooming groove portion11 a 4 extends in a circumferential direction of the cam ring 22, i.e.,extends parallel to the accommodation groove portion 11 a 2. The threefollower pins 21 f and the three follower pins 22 f are inserted intothe three cam grooves 11 a via the linear groove portions 11 a 1thereof, respectively.

In a state where the follower pins 21 f and the follower pins 22 f arerespectively engaged in the accommodation groove portions 11 a 2 (i.e.,in a state where the cam ring 22 is in an accommodationposition/fully-retracted position), a forward rotation of the motor 18causes the rotational ring 20 to rotate in a direction to extend thezoom lens barrel 10 relative to the stationary barrel 11. This causesthe rotational ring 20 to transfer the rotational motion thereof to thecam ring 22 due to the engagement of the three guide keys 22 b of thecam ring 22 in the three rotation-transmission grooves 20 c of therotational ring 20, respectively, so that the rotational ring 20, thebiasing ring 21 and the cam ring 22 rotate together about the opticalaxis O. Further forward rotation of the motor 18 causes each followerpin 21 f of the biasing ring 21 and each follower pin 22 f of the camring 22 to move from the accommodation groove portion 11 a 2 to theposition-changing groove portion 11 a 3, so that the cam ring 22 movesforward in the optical axis direction while rotating about the opticalaxis O. Further forward rotation of the motor 18 causes each followerpin 21 f and each follower pin 22 f to move from the position-changinggroove portion 11 a 3 to the zooming groove portion 11 a 4, so that thecam ring 22 rotates about the optical axis O without further moving inthe optical axis direction in accordance with the cam profile of thezooming groove portion 11 a 4.

As shown in FIG. 12, in a state where both the follower pins 21 f andthe follower pins 22 f are engaged in the accommodation groove portions11 a 2 (i.e., in a state where the cam ring 22 is in the accommodationposition), the three rotation-transmission arms 20 b are fully fitted(accommodated) in the three engaging recesses 22 a with the front endsurface of the circumferential gear portion 20 a of the rotational ring20 being in contact with the rear end surface of the biasing ring 21. Inthis state, the movement of the follower pins 21 f and the follower pins22 f to the zooming groove portion 11 a 4 via the position-changinggroove portion 11 a 3 causes the cam ring 22 and the biasing ring 21 tomove together forwards to enter a photographing position as shown inFIG. 13, with the rotational ring 20 remaining in the rear of thestationary barrel 11.

Thereafter, a reverse rotation of the motor 18 causes the follower pins21 f and the follower pins 22 f to move from the zooming groove portion11 a 4 toward the accommodation groove portions 11 a 2, performing amovement reverse to the above-described movement. At the same time, therotational ring 20, the biasing ring 21 and the cam ring 22 move fromthe photographing state shown in FIG. 13 to the accommodation positionshown in FIG. 12.

In the present embodiment of the zoom lens barrel, the rotational ring20, the biasing ring 21, the cam ring 22 and a barrier drive ring 44 arerotatable elements. The remaining movable elements, except for a secondlens group moving frame 31, linearly move in the optical axis directionwithout rotating about the optical axis O. The second lens group movingframe 31 can slightly rotate about the optical axis O. Such linearlymoving elements and linear guiding mechanisms thereof will behereinafter discussed.

As shown in FIG. 8, the zoom lens barrel 10 is provided between thestationary barrel 11 and the cam ring 22 with the second ring 27 and afirst ring (inner ring) 28 positioned in the second ring 27. The secondring 27, which is positioned just inside the stationary barrel 11, isprovided, on an inner peripheral surface thereof at the rear end of thesecond ring 27, with three bayonet prongs 27 c (only of which appears inFIG. 8) which are engaged with the three bayonet prongs 24 of the camring 22, respectively. Due to the engagement of the three bayonet prongs27 c with the three bayonet prongs 24, the second ring 27 is relativelyrotatable about the optical axis O with respect to the cam ring 22, anddoes not relatively move in the optical axis direction with respect tothe cam ring 22.

As shown in FIG. 1, the second ring 27 is provided, on an outerperipheral surface thereof at the rear end of the second ring 27, withthe three linear guide keys 27 a. The three linear guide keys 27 a areformed on the second ring 27 at equi-angular intervals (intervals of 120degrees) in a circumferential direction of the second ring 27 to berespectively engaged in the three linear guide grooves lid. The secondring 27 is guided linearly in the optical axis direction withoutrotating about the optical axis O with respect to the stationary barrel11 due to the engagement of the three linear guide keys 27 a with thethree linear guide grooves 11 d.

The second ring 27 is provided, on an inner peripheral surface thereofat equi-angular intervals (intervals of 120 degrees) in acircumferential direction of the second ring 27, with three linear guidegrooves 27 b which extend parallel to the optical axis O. The first ring28 is provided, on an outer peripheral surface thereof, at the rear endof the first ring 28 at equi-angular intervals (intervals of 120degrees) in a circumferential direction of the first ring 28, with threecylindrical projections 28 a which are engaged in the three linear guidegrooves 27 b, respectively. The first ring 28 is guided linearly in theoptical axis direction without rotating about the optical axis O withrespect to the second ring 27 due to the engagement of the three linearguide grooves 27 b with the three cylindrical projections 28 a. Each ofthe three cylindrical projections 28 a is provided with a radial hole 28a into which a follower pin 28 f (see FIGS. 8 through 10) ispress-fitted.

The first ring 28 is provided in the vicinity of the front end thereofwith an inner flange 28 b which extends radially inwards and to which abarrier unit 43 and the barrier drive ring 44 are fixed. The first ring28 is provided therein, on a rear surface of the inner flange 28 b, withthree guiding members 28 e (only one of them is indicated in FIGS. 1 and8) which extend in the optical axis direction. The zoom lens barrel 10is provided with a first lens group moving frame 29 which holds thefirst lens group L1 via a first lens group supporting frame 32. Thefirst lens group moving frame 29 is positioned in the first ring 28 tobe surrounded and supported by the three guiding members 28 e to beslidably guided thereby in the optical axis direction. Specifically, thefirst lens group moving frame 29 is provided, on an outer peripheralsurface thereof at the front end of the first lens group moving frame 29at equi-angular intervals in a circumferential direction of the firstlens group moving frame 29, with three linear guide grooves 29 a whichextend parallel to the optical axis O, and three linear guide keys 28 dwhich are formed on inner surfaces of the three guiding members 28 e toextend parallel to the optical axis O are slidably engaged in the threelinear guide grooves 29 a, respectively, so that the first lens groupmoving frame 29 is guided linearly in the optical axis direction withoutrotating about the optical axis O by the first ring 28.

The inner flange 28 b of the first ring 28 is provided on a rear facethereof, at equi-angular intervals (intervals of 120 degrees) in acircumferential direction of the first ring 28, with threespring-support protrusions 28 c (see FIGS. 8 through 10), and the firstlens group moving frame 29 is provided, on a front end surface thereofat positions thereon facing the set of spring support protrusions 28 c,with three spring-support recesses 29 b which are formed at equi-angularintervals in a circumferential direction of the first lens group movingframe 29. Three helical compression springs 30 serving as a biasingdevice are inserted to be held between the three spring-supportprotrusions 28 c and the three spring-support recesses 29 b,respectively, to press the first lens group moving frame 29 rearwards inthe optical axis direction. The first lens group moving frame 29 isprovided at the rear end thereof with three cutout portions 29 i inwhich three engaging projections 31 h formed on an outer peripheralsurface of the second lens group moving frame 31 at the rear end thereofare positioned, respectively (see FIG. 24).

The second lens group moving frame 31 that supports the second lensgroup L2 is fitted in the first lens group moving frame 29. The secondlens group moving frame 31 is provided, on an outer peripheral surfacethereof at the front end of the outer peripheral surface, with threelinear guide keys 31 a (see FIGS. 1 and 2) which are slidably engaged inthree linear guide grooves of four linear guide grooves 29 c (only oneof them appears in each of FIGS. 21A through 21J) which are formed on aninner peripheral surface of the first lens group moving frame 29 toextend parallel to the optical axis O. Due to the engagement of thethree linear guide keys 31 a with the three linear guide grooves 29 c,the second lens group moving frame 31 is guided linearly withoutrotating about the optical axis O by the first lens group moving frame29.

As can be understood from the above description, according to the abovedescribed linear guiding mechanisms, the second ring 27 is guidedlinearly in the optical axis direction without rotating about theoptical axis O via the stationary barrel 11, the first ring 28 is guidedlinearly in the optical axis direction without rotating about theoptical axis O via the second ring 27, the first lens group moving frame29 is guided linearly in the optical axis direction without rotatingabout the optical axis O via the first ring 28, and the second lensgroup moving frame 31 is guided linearly in the optical axis directionwithout rotating about the optical axis O via the first lens groupmoving frame 29, in that order from the outside to the inside of thezoom lens barrel 10.

The first lens group moving frame 29 is provided at the front endthereof with an inner flange 29 g which extends radially inwards to forma circular aperture having the center thereof about the optical axis O.As shown in FIG. 1, a female thread portion 29 d is formed on an innerperipheral face of the inner flange 29 g. A lens pressure ring 32 a isfixed to the rear end surface of the first lens group supporting frame32 that holds the first lens group L1. The first lens group supportingframe 32 is provided on an outer peripheral surface thereof with a malethread portion which is in mesh with the female thread portion 29 d ofthe inner flange 29 g. The first lens group supporting frame 32 iscemented to the first lens group moving frame 29 by adhesive after thethread engagement position of the male thread portion of the first lensgroup supporting frame 32 with respect to the female thread portion 29 dof the inner flange 29 g has been adjusted during assembly.

As shown in FIG. 2, the second lens group moving frame 31 is provided ona rear end wall thereof, at the center of the rear end wall, with acylindrical portion 31 b, the front and rear ends thereof being open. Anannular recess 31 c is formed between an outer circumferential wall ofthe second lens group moving frame 31 and the cylindrical portion 31 b.As shown in FIGS. 1 and 2, the second lens group L2 consists of twoseparate lens elements, a spacer ring 33 being positioned therebetween.The two lens elements of the second lens group L2 together with thespacer ring 33 are fitted in the cylindrical portion 31 b to be fixedtherein. As shown in FIGS. 5 and 7, the second lens group moving frame31 is provided on the rear end wall thereof with a first cutout portion31 d in the shape of an arc, and is provided, across the outercircumferential wall and the rear end wall of the second lens groupmoving frame 31, with a second cutout portion 31 e which is larger thanthe first cutout portion 31 d.

The zoom lens barrel 10 is provided in the annular recess 31 c of thesecond lens group moving frame 31 with a shutter unit 36. As shown inFIG. 2, a shutter support ring 35, positioned between the shutter unit36 and the second lens group moving frame 31, is provided on a frontsurface of a ring portion 35 a thereof with a support member 35 b whichprojects forward from the ring portion 35 a to support the shutter unit36. The shutter support ring 35 is provided on a rear surface of thering portion 35 a with a flexible printed wiring board (flexible PWB)fixing member 35 c which extends rearward from the ring portion 35 a.The shutter support ring 35 is provided at the center of the ringportion 35 a with a circular aperture 35 d in which the cylindricalportion 31 b is fitted. The shutter support ring 35 is loosely fitted inthe annular recess 31 c to be freely rotatable about the optical axis Owith respect to the second lens group moving frame 31 with thecylindrical portion 31 b being fitted in the circular aperture 35 d andwith the flexible PWB fixing member 35 c extending through the rear endwall of the second lens group moving frame 31 through the first cutoutportion 31 d. As shown in FIG. 2, the shutter support ring 35 isprovided on the support member 35 b with a linear guide key 35 eextending parallel to the optical axis O. The linear guide key 35 e isengaged in one of the four linear guide grooves 29 c, in which thelinear guide key 31 a which is not engaged, to be freely and slidablymovable therein in the optical axis direction. Accordingly, the shuttersupport ring 35 is not rotatable about the optical axis O since thefirst lens group moving frame 29 is not rotatable about the optical axisO either.

The shutter unit 36 is mounted on the support member 35 b, and is fixedto the support member 35 b by two set screws 35 f as shown in FIG. 2.

The second lens group moving frame 31 is provided, on the outercircumferential wall thereof in the vicinity of the front end of theouter circumferential wall, with three engaging holes 31 i positioned ona circle about the optical axis O. A shutter pressure plate 37positioned in front of the shutter unit 36 is provided, on an outerperipheral surface thereof, with three engaging projections 37 a whichare elastically engaged in the three engaging holes 31 i, respectively.The shutter support ring 35 and the shutter unit 36 are prevented fromcoming off the annular recess 31 c by the shutter pressure plate 37 in amanner such that the shutter pressure plate 37 closes the front end ofthe annular recess 31 c with the three engaging projections 37 a beingengaged in the three engaging holes 31 i (see FIGS. 4 and 6).

The shutter pressure plate 37 is provided on a front surface thereofwith three engaging protrusions 37 b. A low-frictional ring sheet 38 isfixed to a front annular surface of the shutter pressure plate 37 to beheld between the three engaging protrusions 37 b and the front annularsurface of the shutter pressure plate 37. The low-frictional ring sheet38 is made of a low-frictional material such as a tetrafluoroethyleneresin.

The shutter unit 36 is provided with shutter blades 36 a (see FIGS. 8through 10). The shutter unit 36 drives the shutter blades 36 a to openand close in accordance with information on an object brightness. Thezoom lens barrel 10 is provided therein with a flexible printed wiringboard (flexible PWB) F, one end (front end) of which is fixed to theshutter unit 36 (see FIGS. 8 through 10). A drive signal is given to theshutter unit 36 via the flexible PWB F. As shown in FIGS. 8 through 10,the flexible PWB F extends rearward from the shutter unit 36 on an uppersurface of the flexible PWB fixing member 35 c therealong, and bendsradially inwards to subsequently extend forward. Subsequently, theflexible PWB F is fixed to a lower surface of the flexible PWB fixingmember 35 c with adhesive tape, and bends radially inwards to extendrearward. Subsequently, the flexible PWB F extends through the CCDholding frame 13 via a through-slot 13 a (see FIG. 1) formed thereon,and bends radially outwards to extend upwards along a rear surface ofthe CCD holding frame 13. Subsequently, flexible PWB F bends to extendforward and above the stationary barrel 11. The second lens group movingframe 31 is provided on a rear surface thereof with a flexible PWBsupport member 31 j (see FIG. 8) for supporting (taking up) the slack ofthe flexible PWB.

The zoom lens barrel 10 is provided with a third lens frame 39 to whichthe third lens group L3 is fixed. As shown in FIG. 1, the third lensframe 39 is guided in the optical axis direction via a pair of linearguide rods 40 which extend parallel to the optical axis O. The front andrear ends of each linear guide rod 40 are fixed to the shaft holdingmember 12 and the CCD holding frame 13, respectively. The third lensframe 39 is driven to move in the optical axis direction by rotation ofa feed screw shaft 41 which is driven forward and backward by a stepmotor (not shown) in accordance with information on a photographingdistance.

A zooming operation is carried out by moving the first and second lensgroups L1 and L2 (the first and second lens group moving frames 29 and31) in the optical axis direction relative to the third lens group L3while varying the distance therebetween. The cam ring 22 is provided, onan inner peripheral surface thereof at equi-intervals (intervals of 120degrees) in a circumferential direction of the cam ring 22, with threelens-drive cam grooves (first cam grooves) C1. The first lens groupmoving frame 29 and the second lens group moving frame 31, which areguided linearly in the optical axis direction without rotating about theoptical axis O, move in the optical axis direction by rotation of thecam ring 22 in accordance with the profiles of the lens-drive camgrooves C1. FIG. 20 shows a developed view of the lens-drive cam groovesC1. The zoom lens barrel 10 is characterized in that each lens-drive camgroove C1 is formed as a continuous bottomed groove to have respectivecam groove portions for the first and second lens groups L1 and L2, andthat the first and second lens groups L1 and L2 are released from theconstraints of the three lens-drive cam grooves C1 at their respectiveaccommodation positions so that the first and second lens groups L1 andL2 can be accommodated to be positioned close to each other until thefirst lens group supporting frame 32 and the second lens group movingframe 31 come into contact with each other.

Namely, three follower pins 29 f which are projected radially outwardsfrom the first lens group moving frame 29 and three follower pins 31 fwhich are projected radially outwards from the second lens group movingframe 31 are slidably engaged in the three lens-drive cam grooves C1,respectively. Each lens-drive cam groove C1, which is formed as acontinuous bottomed groove, has a function to move the first and secondlens groups L1 and L2 in their respective zoom paths. Unlike the presentembodiment of the zoom lens barrel 10, in a conventional zoom lensbarrel having a cam ring for driving a plurality of movable lens groups,a set of cam grooves is necessary for each of the plurality of movablelens groups.

As shown in FIG. 20, each lens-drive cam groove C1 is provided at oneend thereof with an insertion end Cle via which one of the threefollower pins 29 f of the first lens group moving frame 29 and one ofthe three follower pins 31 f of the second lens group moving frame 31are inserted into the lens-drive cam groove C1. Each lens-drive camgroove C1 is further provided with a first-lens-group zooming section(front lens group moving section/photographing section) C1Z1, asecond-lens-group zooming section (rear lens group movingsection/photographing section) C1Z2, a first-lens-group accommodationportion C1A1, a connecting portion C1A2, and asecond-lens-group-accommodation end portion C1S2, in that order from theinsertion end C1 e. The opposite ends (left and right ends as viewed inFIG. 20) of the first-lens-group zooming section C1Z1 determines atelephoto extremity Z1T and a wide-angle extremity Z1W of the first lensgroup L1, respectively. The opposite ends (left and right ends as viewedin FIG. 20) of the second-lens-group zooming section C1Z2 determines atelephoto extremity Z2T and a wide-angle extremity Z2W of the secondlens group L2, respectively. As shown in FIG. 20, in this particularembodiment of the zoom lens barrel 10, the angle of rotation of the camring 22 when driving each of the first and second lens group movingframes 29 and 31 from the accommodation position to the telephotoextremity is predetermined at 178 degrees, and the angle of rotation ofthe cam ring 22 when driving each of the first and second lens groupmoving frames 29 and 31 from the wide-angle extremity to the telephotoextremity is determined at 70 degrees.

As shown in FIG. 20, the width of the first-lens-group accommodationportion C1A1 of the lens-drive cam groove C1 in the optical axisdirection (the vertical direction as viewed in FIG. 20) is greater thanthe width of the other portions of the lens-drive cam groove C1 so thatthe associated follower pin 29 f can move freely in the first-lens-groupaccommodation portion C1A1. Namely, the first-lens-group accommodationportion C1A1 extends in a circumferential direction of the cam ring 22,and also widens in the optical axis direction to form a clearance forthe associated follower pin 29 f of the first lens group moving frame 29to be movable in the optical axis direction by an amount of movementcorresponding to the range of adjustment of the thread engagementposition of the male thread portion of the first lens group supportingframe 32 with respect to the female thread portion 29 d of the innerflange 29 g. The second-lens-group-accommodation end portion C1S2 of theconnecting portion C1A2, which is one end of the connecting portion C1A2on the side opposite from the first-lens-group accommodation portionC1A1, is shaped to form a clearance for the associated follower pin 31 fof the second lens group moving frame 31 to be slightly movable both inthe optical axis direction and in a circumferential direction of the camring 22 when the associated follower pin 31 f is engaged in thesecond-lens-group-accommodation end portion C1S2.

As shown in FIG. 16, which shows a developed view of the outerperipheral surface of the cam ring 22, the three engaging recesses 22 aof the cam ring 22 are formed so as not to interfere with the three camgrooves (second cam grooves) C2, which are formed on an outer peripheralsurface of the cam ring 22 so as to have a substantially V-shapedprofile (cam path) in a development view as shown in FIG. 16. The frontend of each engaging recess 22 a is positioned just behind an adjacentpeak (frontmost peak portion) C2E of the associated cam groove C2 whichis the frontmost portion of the cam groove C2. The front end of eachengaging recess 22 a is formed to have an oblique surface 22 a-1 so thateach engaging recess 22 a does not interfere with the associated camgrooves C2. The front end portion of each rotation-transmission arm 20 bis formed to have an oblique cutout portion 20 d which is shaped tocorrespond to the oblique surface 22 a-1 of the engaging recess 22 a(See FIG. 11B). Furthermore, as shown in FIG. 16, the three guide keys22 b are provided in the close vicinity of the three bayonet prongs 24,and are each formed so as to extend along an extension line Z whichextends parallel to the optical axis through the corresponding peak C2E.In other words, the three guide keys 22 b are each provided at acircumferential position of longest portion of a corresponding engagingrecess 22 a in a direction parallel to the optical axis. Accordingly,since the three guide keys 22 b can be made long in the directionparallel to the optical axis, the linear guidance precision thereof canbe increased.

The relative angular positions of the three follower pins 29 f and thethree follower pins 31 f about the optical axis O are determined so thateach follower pin 29 f and each follower pin 31 f are respectivelypositioned in the first-lens-group accommodation portion C1A1 and thesecond-lens-group-accommodation end portion C1S2 of the connectingportion C1A2 when the cam ring 22 is positioned in an accommodationposition thereof (see FIG. 20). The first-lens-group accommodationportion C1A1 and the second-lens-group-accommodation end portion C1S2 ofthe connecting portion C1A2, to some extent, do not constrain movementof the associated follower pins 29 f and 31 f, respectively. Namely,each follower pin 29 f and each follower pin 31 f can move in thefirst-lens-group accommodation portion C1A1 and thesecond-lens-group-accommodation end portion C1S2 of the connectingportion C1A2, respectively, in the optical axis direction because of theclearance formed between each groove portion and the associated followerpin. This clearance contributes to further miniaturization of the lengthof the zoom lens barrel 1 in an accommodation position thereof.

Since the three helical compression springs 30 press the first lensgroup moving frame 29 rearwards in the optical axis direction asdescribed above, the lens pressure ring 32 a that is supported by thefirst lens group moving frame 29, can retract up to a mechanicallycontacting point P (see FIG. 8) where the lens pressure ring 32 a comesin contact with the low-frictional ring sheet 38 that is fixed to thefront surface of the shutter pressure plate 37, due to the clearancebetween the first-lens-group accommodation portion C1A1 of eachlens-drive cam groove C1 of the cam ring 22 and the associated followerpin 29 f of the first lens group moving frame 29. Likewise, the flexiblePWB support member 31 j of the second lens group moving frame 31 canretract up to a mechanically contacting point Q (see FIG. 8) where thesecond lens group moving frame 31 comes in contact with the third lensframe 39 due to a clearance between the second-lens-group-accommodationend portion C1S2 of the connecting portion C1A2 of each lens-drive camgroove C1 of the cam ring 22 and the associated follower pin 31 f of thesecond lens group moving frame 31.

Due to such structures of the mechanically contacting points P and Q,the length of the zoom lens barrel 10 in an accommodation positionthereof is successfully reduced as compared with a conventional zoomlens barrel in which the respective accommodation positions of first andsecond lens groups which correspond to the first and second lens groupsL1 and L2 of the present embodiment of the zoom lens barrel areprecisely determined by associated cam grooves. Furthermore, as shown inFIG. 8, the third lens frame 39 can retract up to a mechanicallycontacting point R where the third lens frame 39 comes in contact withthe CCD holding frame 13 while compressing a helical compression spring42, which is fitted on the feed screw shaft 41 to be positioned betweenthe third lens frame 39 and the CCD holding frame 13 to bias the thirdlens frame 39 forward.

FIG. 8 shows an accommodation position of the zoom lens barrel 10 wherethe first lens group moving frame 29 (lens pressure ring 32 a) is incontact with the low-frictional ring sheet 38, where the second lensgroup moving frame 31 is in contact with the third lens frame 39, andwhere the third lens frame 39 is in contact with the CCD holding frame13.

The amount of rearward movement of the first lens group moving frame 29relative to the second lens group moving frame 31 depends on theposition of the first lens group supporting frame 32 relative to thefirst lens group moving frame 29, since the position of the second lensgroup supporting frame 32 relative to the first lens group moving frame29 varies by an adjustment of the thread engagement position of the malethread portion of the first lens group supporting frame 32 with respectto the female thread portion 29 d of the inner flange 29 g duringassembly. Such a variation due to the adjustment is absorbed byextension or compression of the helical compression springs 30 so thatthe zoom lens barrel 10 can be accommodated with the lens pressure ring32 a, the second lens group moving frame 31, and the third lens frame 39being in contact with the low-frictional ring sheet 38, the third lensframe 39, and the CCD holding frame 13 at the mechanically contactingpoints P, Q and R, respectively.

If the cam ring 22 rotates in a direction from the accommodationposition toward a photographing position in the zooming groove portion11 a 4, each follower pin 29 f of the first lens group moving frame 29which is engaged in the first-lens-group accommodation portion C1A1moves from the first-lens-group accommodation portion C1A1 to thefirst-lens-group zooming section C1Z1 via the second-lens-group zoomingsection C1Z2, while each follower pin 31 f of the second lens groupmoving frame 31 which is engaged in the connecting portion C1A2 movesfrom the connecting portion C1A2 to the second-lens-group zoomingsection C1Z2 via the first-lens-group accommodation portion C1A1.Accordingly, the second-lens-group zooming sections C1Z2 of the threelens-drive cam grooves C1 that are used for driving the three followerpins 31 f of the second lens group moving frame 31 are used as merepassing sections for the three follower pins 29 f of the first lensgroup moving frame 29 via which the three follower pins 29 f move fromthe first-lens-group accommodation position to the photographingposition. The above-described structure which provides such passingsections is advantageous to reduce the number of cam grooves which areto be formed on the cam ring 22, which is in turn advantageous to reducethe angle of inclination of each cam groove with respect to acircumferential direction of the cam ring 22.

The first ring 28 moves in the optical axis direction independent of thefirst lens group moving frame 29 in a moving path which is substantiallythe same as the moving path of the first lens group moving frame 29.Accordingly, the cam ring 22 is provided, on an outer peripheral surfaceat equi-intervals (intervals of 120 degrees) in a circumferentialdirection thereof, with the three cam grooves C2 (see FIGS. 16 through19). The first ring 28 is provided, on an inner peripheral surface atequi-intervals in a circumferential direction thereof, with threefollower pins 28 f which are slidably engaged in the three cam groovesC2 of the cam ring 22, respectively. The profiles of the cam grooves C2resemble those of the lens-drive cam grooves C1. As shown in FIG. 17A,each cam groove C2 is provided at one end thereof with an insertion endC2 e via which one of the three follower pins 28 f of the first ring 28is inserted into the cam groove C2. Each cam groove C2 is furtherprovided with a first section C2Z1 which corresponds to thefirst-lens-group zooming section C1Z1, a second section C2Z2 whichcorresponds to the second-lens-group zooming section C1Z2, and a barrierdrive section C2B. The barrier drive section C2B extends in acircumferential direction of the cam ring 22, so that the cam ring 22rotates about the optical axis O without moving in the optical axisdirection relative to the first ring 28 as long as each follower pin 28f is engaged in the barrier drive section C2B. As shown in FIG. 16, inthis particular embodiment of the zoom lens barrel 10, the angle ofrotation of the cam ring 22 when driving the first ring 28 from theaccommodation position to the telephoto extremity is predetermined at178 degrees, and the angle of rotation of the cam ring 22 when drivingthe first ring 28 from the wide-angle extremity to the telephotoextremity is determined at 70 degrees.

By providing the first ring 28, which extends forward so that an outerperipheral surface thereof is exposed to the outside of the zoom lensbarrel 10, as an element separate from the first lens group moving frame29, and by guiding the first ring 28 in the optical axis direction via acam mechanism independent of the first lens group moving frame 29 asdescribed above, external forces applied to the first ring 28 can beprevented from being transferred to the first lens group L1 via thefirst lens group moving frame 29, which in turn prevents deteriorationin optical performance of the zoom lens barrel 10 due to eccentricity ofthe optical axis of the first lens group L1. In addition, the structureof the cam ring 22 wherein the three lens-drive cam grooves C1 and thethree cam grooves C2, whose cam profiles are similar (though differingslightly in shape) to each other, are formed on the cam ring 22 inslightly different positions thereon in the optical axis direction doesnot increase the wall thickness of the cam ring 22. Moreover, externalforces applied to the first ring 28 rearward in the optical axisdirection can be received by the first lens group moving frame 29 viathe three follower pins 29 f.

Furthermore, since the three follower pins 28 f, which are respectivelyengaged in the three cam grooves C2, and the three follower pins 29 f,which are respectively engaged in the three lens-drive cam grooves C1,are respectively aligned side by side in a direction parallel to theoptical axis O, the strength of the spring force of the three helicalcompression springs 30 that are held between the first ring 28 and thefirst lens group moving frame 29 to bias the first ring 28 and the firstlens group moving frame 29 in opposite directions away from each othervaries little even if the cam ring 22 rotates relative to the first ring28 and the first lens group moving frame 29.

As shown in FIG. 1, the barrier unit 43 includes a barrier blade supportfront plate 45, a pair of barrier blades 46, two torsion springs 47 anda barrier blade support rear plate 48, and is fixed to the front end ofthe first ring 28 to be positioned therein, in front of the inner flange28 b. The barrier drive ring 44 is positioned in the first ring 28 andheld between the barrier unit 43 and the inner flange 28 b of the firstring 28 to be rotatable freely about the optical axis O. The cam ring 22is provided at the front end thereof with three recesses 22 k (see FIGS.16 through 20). The barrier drive ring 44 is provided on an outerperipheral surface thereof with three engaging portions 44 a. The camring 22 is provided at one end of each recesses 22 k with a rotationtransfer face 22 d which extends parallel to the optical axis O andextends through a corresponding circumferential slot 28 z (see FIG. 1)formed on the inner flange 28 b of the first ring 28. As shown in FIGS.16 through 20, the three recesses 22 k are formed on the cam ring 22 atportions thereon other than the portions where the three cam grooves C2are formed.

As shown in FIG. 1, the barrier unit 43, which includes the barrierblade support front plate 45, the pair of barrier blades 46, the twotorsion springs 47 and the barrier blade support rear plate 48, isformed as a single assembly in advance. The barrier blade support frontplate 45 is provided at the center thereof with a photographing aperture45 a, and is further provided, on a rear surface thereof on oppositesides of the photographing aperture 45 a, with two bosses (not shown),respectively, which extend rearwards. Each barrier blade 46 is providedat one end thereof with a hole in which one of the two bosses is engagedso that each barrier blade 46 is rotatable about the associated boss.The two torsion springs 47 bias the pair of barrier blades 46 to rotatein opposite rotational directions to shut the pair of barrier blades 46,respectively. The pair of barrier blades 46 are supported between thebarrier blade support front plate 45 and the barrier blade support rearplate 48. The barrier blade support rear plate 48 is provided at thecenter thereof with a central aperture which is aligned with thephotographing aperture 45 a in the optical axis direction, and isfurther provided on opposite sides of the central aperture with twoslots 48 a. Each barrier blade 46 is provided in the vicinity of theassociated boss with an engaging projection 46 a (only one of whichappears in FIGS. 8 through 10) which extends rearward, toward thebarrier drive ring 44, to pass through the associated slot 48 a of thebarrier blade support rear plate 48.

The barrier drive ring 44 is biased to rotate in a direction to open thepair of barrier blades 46 by a helical extension spring 49 whoseopposite ends are hooked on an engaging projection 44 b formed on thebarrier drive ring 44 and an engaging projection 28 h formed on a frontsurface of the inner flange 28 b of the first ring 28. The spring forceof the helical extension spring 49 is greater than the total springforce of the two torsion springs 47. The two drive projections 44 c ofthe barrier drive ring 44 come into contact with the two engagingprojections 46 a of the pair of barrier blades 46 to open the pair ofbarrier blades 46, respectively, when the barrier drive ring 44 is in afully rotated position thereof due to the spring force of the helicalextension spring 49. If the barrier drive ring 44 is rotated in adirection to close the pair of barrier blades 46 against the springforce of the helical extension spring 49, the two drive projections 44 crespectively move away from the two engaging projections 46 a of thepair of barrier blades 46 so that the pair of barrier blades 46 areclosed by the spring force of the two torsion springs 47.

The three rotation transfer faces 22 d of the cam ring 22 respectivelycome into contact with the three engaging portions 44 a of the barrierdrive ring 44 to press the three engaging portions 44 a against thespring force of the helical extension spring 49 to rotate the barrierdrive ring 44. When the cam ring 22 is in the accommodation positionthereof, the three rotation transfer faces 22 d are respectively incontact with the three engaging portions 44 a of the barrier drive ring44 via the three circumferential slots 28 z formed on the inner flange28 b of the first ring 28. The barrier drive ring 44 is rotated aboutthe optical axis O against the spring force of the helical extensionspring 49 to close the pair of barrier blades 46. If the cam ring 22rotates about the optical axis O in a barrier opening direction(counterclockwise as viewed from the front of the zoom lens barrel 10)with respect to the first ring 28, with the three follower pins 28 fbeing respectively engaged within the barrier drive sections C2B of thethree cam grooves C2 of the cam ring 22, the three rotation transferfaces 22 d are respectively disengaged from the three engaging portions44 a of the barrier drive ring 44 so that the barrier drive ring 44 isrotated in a direction to open the pair of barrier blades 46 by thespring force of the helical extension spring 49.

The barrier unit 43 having the above described structure is fitted intothe front end opening of the first ring 28 from the front thereof. Thebarrier blade support front plate 44 is provided on an outer peripheraledge thereof with a plurality of engaging portions which arerespectively engaged with a corresponding plurality of hooks (not shown)formed on an inner peripheral surface of the front end opening of thefirst ring 28 to prevent the barrier unit 43 from coming off the frontof the first ring 28. The barrier drive ring 44 is held between thebarrier unit 43 and the inner flange 28 b of the first ring 28 to berotatable about the optical axis O.

As has been described above, the zooming groove portion 11 a 4 (see FIG.28) of each cam groove 11 a of the stationary barrel 11 extends in acircumferential direction of the stationary barrel 11 and does notextend in the optical axis direction. Therefore, the cam ring 22 rotatesabout the optical axis O without moving in the optical axis directionwhen the three follower pins 22 f of the cam ring 22 and the threefollower pins 21 f of the biasing ring 21 follow the three zoominggroove portions 11 a 4 of the three cam grooves 11 a in the zoomingsection, respectively. In the zooming section that is determined by thezooming groove portion 11 a 4, it is necessary to remove backlash andplay between the three follower pins 22 f and the zooming grooveportions 11 a 4 of the three cam grooves 11 a.

To remove such backlash and play, each of the three follower pins 21 fand the associated one of the three follower pins 22 f are engaged in acommon cam groove of the three cam grooves 11 a of the stationary barrel11 at slightly different circumferential positions as shown in FIG. 28,and each follower pin 21 f of the biasing ring 21 and each follower pin22 f of the cam ring 22 are pressed against a rear side edge of theassociated cam groove 11 a and a front side edge of the same cam groove11 a, respectively, by the spring force of the three compression helicalsprings 26. Due to this structure wherein the three follower pins 22 fof the cam ring 22 are pressed against the front side edges of thezooming groove portion 11 a 4 of the three cam grooves 11 a when engagedin the zooming groove portion 11 a 4, backlash and play between thethree follower pins 22 f and the zooming groove portions 11 a 4 of thethree cam grooves 11 a are removed.

In addition to the above described structures wherein the three linearguide grooves 29 c are formed on an inner peripheral surface of thefirst lens group moving frame 29 while the three linear guide keys 31 a,which are respectively engaged in the three linear guide grooves 29 c,are formed on an outer peripheral surface of the second lens groupmoving frame 31, three circumferential recesses 29 h (see FIGS. 21Athrough 21J) are formed on the first lens group moving frame 29 at thefront ends of the three linear guide grooves 29 c, respectively. Eachcircumferential recess 29 h allows the associated linear guide key 31 aof the second lens group moving frame 31 to move therein in acircumferential direction about the optical axis O, i.e., allows thesecond lens group moving frame 31 to rotate about the optical axis Orelative to the first lens group moving frame 29 in a rangecorresponding to the circumferential length of the circumferentialrecess 29 h. The second lens group moving frame 31 can rotate about theoptical axis O relative to the first lens group moving frame 29 alongthe three circumferential recesses 29 h only when the second lens groupmoving frame 31 is in the vicinity of the accommodation positionthereof.

Note that the first lens group moving frame 29 is provided on the innerflange 29 g thereof with three circumferential slots 29 j (see FIGS. 24through 27). The second lens group moving frame 31 is provided at thefront end thereof with three front projecting portions 31 g onrespective outer surfaces on which the three linear guide keys 31 a areformed, respectively. When each linear guide key 31 a is positioned inthe associated circumferential recess 29 h, i.e., when the second lensgroup L2 is in the vicinity of the accommodation position thereof, thethree front projecting portions 31 g of the second lens group movingframe 31 extend through the inner flange 29 g of the first lens groupmoving frame 29 to project forward from the inner flange 29 g via thethree circumferential slots 29 j, respectively. Accordingly, allowingthe three linear guide keys 31 a to project forward from the innerflange 29 g through the three circumferential slots 29 j, respectively,achieves the short length of the zoom lens barrel 10 in an accommodationposition shown in FIG. 8.

In a state where the zoom lens barrel 10 is in an accommodationposition, i.e., where each of the three follower pins 29 f of the firstlens group moving frame 29 is engaged in the first-lens-groupaccommodation portion C1A1 of the associated lens-drive cam groove C1 asshown in FIG. 21A, a rotation of the cam ring 22 in a direction toextend the zoom lens barrel 10 (in a direction indicated by an arrow “X”in FIGS. 21A through 21J, i.e., counterclockwise as viewed from thefront of the zoom lens barrel 10) causes each follower pin 29 f of thefirst lens group moving frame 29 to move slightly from thefirst-lens-group accommodation portion C1A1 toward the second-lens-groupzooming section C1Z2 of the associated lens-drive cam groove C1 as shownin FIG. 21B. At this time, each follower pin 31 f of the second lensgroup moving frame 31 does not move out from thesecond-lens-group-accommodation end portion C1S2 of the connectingportion C1A2.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move slightly toward the second-lens-group zooming section C1Z2while moving rearward slightly in the optical axis direction as shown inFIG. 21C. At the same time, since each follower pin 31 f does not moveout from the second-lens-group-accommodation end portion C1S2 of theconnecting portion C1A2, front end surfaces (upper end surfaces asviewed in FIG. 21C) of the three cutout portions 29 i of the second lensgroup moving frame 29 come into contact with front end surfaces of thethree engaging projections 31 h of the second lens group moving frame31, respectively, as shown in FIG. 21C.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move slightly toward the second-lens-group zooming section C1Z2while moving rearward (downward as viewed in FIG. 21D) in the opticalaxis direction so that the front end surfaces of the three cutoutportions 29 i press the three engaging projections 31 h rearward in theoptical axis direction, respectively, to move each follower pin 31 f ofthe second lens group moving frame 31 in the connecting portion C1A2from the second-lens-group-accommodation end portion C1S2 thereof towardthe first-lens-group accommodation portion C1A1 as shown in FIG. 21D.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tomove forward in the second-lens-group zooming section C1Z2 in a leftoblique direction with respect to the cam ring 22 as viewed in FIG. 21E,so that the three cutout portions 29 i are respectively disengaged fromthe three engaging projections 31 h, and at the same times rear endsurfaces of the three circumferential recesses 29 h respectively comeinto contact with rear end surfaces of the three linear guide keys 31 aas shown in FIG. 21E.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move forward in the second-lens-group zooming section C1Z2 inthe same left oblique direction with respect to the cam ring 22 so thatthe rear end surfaces of the three circumferential recesses 29 hrespectively press the rear end surfaces of the three linear guide keys31 a rearward in the optical axis direction, to thereby move eachfollower pin 31 f of the second lens group moving frame 31 in theconnecting portion C1A2 back toward the second-lens-group-accommodationend portion C1S2 thereof as shown in FIG. 21F. At this time, each linearguide keys 31 a of the second lens group moving frame 31 is positionedin the associated linear guide groove 29 c of the first lens groupmoving frame 29 in the vicinity of the front end thereof.

During the time the zoom lens barrel 10 moves from the position shown inFIG. 21A to the position shown in FIG. 21F, each linear guide keys 31 aof the second lens group moving frame 31 rotates in the associatedcircumferential recess 29 h in a circumferential direction of the firstlens group moving frame 29 with respect to the first lens group movingframe 29. Rotating the second lens group moving frame 31 with respect tothe first lens group moving frame 29 in such a manner makes it possiblefor the first lens group moving frame 29 to move forward smoothlywithout interfering with the second lens group moving frame 31. Thesecond lens group moving frame 31 rotates about the optical axis O withrespect to the first lens group moving frame 29 by 39 degrees (see FIG.20) when the zoom lens barrel 10 moves from the position shown in FIG.21A to the position shown in FIG. 21F.

Further rotational movement of the cam ring 22 in the same direction Xcauses each follower pin 29 f of the first lens group moving frame 29 tofurther move forward in the second-lens-group zooming section C1Z2 inthe same left oblique direction with respect to the cam ring 22 so thateach linear guide keys 31 a of the second lens group moving frame 31 isproperly engaged in the associated linear guide groove 29 c as shown inFIG. 21G. Thereafter, the first lens group moving frame 29 and thesecond lens group moving frame 31 are prohibited from rotating relativeto each other, while each follower pin 29 f and the associated one ofthe three follower pins 31 f move in the associated one of the threelens-drive cam grooves C1 in a direction to the left as viewed in FIG.21G while maintaining a space between the follower pin 29 f and thefollower pin 31 f in a circumferential direction.

Subsequently, if the cam ring 22 continues to rotate in the direction Xwith each linear guide keys 31 a of the second lens group moving frame31 being engaged in the associated linear guide groove 29 c of the firstlens group moving frame 29, the first lens group moving frame 29 and thesecond lens group moving frame 31 move linearly in the optical axisdirection without rotating about the optical axis O while changing aspace in the optical axis therebetween by the movement of the threefollower pins 29 f and the three follower pins 31 f in the threelens-drive cam grooves C1 in a direction toward the left as shown inFIGS. 21H through 21I. Consequently, each follower pin 29 f and theassociated one of the three follower pins 31 f reach their respectivewide-angle extremities in the associated one of the three lens-drive camgrooves C1 as shown in FIG. 21J.

Although not shown in the drawings, each follower pin 29 f and theassociated one of the three follower pins 31 f reach their respectivetelephoto extremities in the associated one of the three lens-drive camgrooves C1 while maintaining a space therebetween in a circumferentialdirection if the cam ring 22 further continues rotating in the samedirection X.

On the other hand, in a state where the zoom lens barrel 10 is in aphotographing position, if the cam ring 22 rotates in a direction toretract the zoom lens barrel 10, i.e., in a direction opposite to thedirection X, each follower pin 29 f and each follower pin 31 f move inan order reverse to the above described order, and return to thefirst-lens-group accommodation portion C1A1 and the connecting portionC1A2, respectively.

FIG. 22 is a graph showing variations of the angle of rotation of thesecond lens group moving frame 31 with respect to the cam ring 22 from astate where the second lens group moving frame 31 is in an accommodationposition to a state immediately after the three linear guide keys 31 aare respectively engaged in the three linear guide grooves 29 c, i.e.,from the position shown in FIG. 21A to the position shown in FIG. 21F.FIG. 23 is a graph showing the relationship between the amount ofdisplacement of the first lens group moving frame 29 from theaccommodation position thereof (represented by “0” in FIG. 23) in theoptical axis direction and the angle of rotation of the cam ring 22, andfurther showing the relationship between the amount of displacement ofthe second lens group moving frame 31 from the accommodation positionthereof (represented by “0” in FIG. 23) in the optical axis directionand the angle of rotation of the cam ring 22. In each of FIGS. 22 and23, (a), (b), (c), (d), (e) and (f) represent the rotational angles ofthe cam ring 22 in FIGS. 21A, 21B, 21C, 21D, 21E and 21F, respectively.The term “Limit Angle” shown in each of FIGS. 22 and 23 represents aspecific angle of rotation of the cam ring 22, wherein the first andsecond lens group moving frames 29 and 31 cannot reach their respectivetelephoto extremities when the three linear guide keys 31 a do not enterthe associated linear guide groove 29 c by the time the cam ring 22 hasrotated to the specific angle of rotation of the cam ring 22.

When the first and second lens group moving frames 29 and 31 rotaterelative to each other at their respective accommodation positions,friction (frictional resistance) is produced between the lens pressurering 32 a, which is supported by the first lens group moving frame 29,and the front surface of the shutter pressure plate 37, which issupported by the second lens group moving frame 31 via the shutter unit36, if a low-frictional element such as the low-frictional ring sheet 38is not fixed to the front surface of the shutter pressure plate 37,unlike the present invention. Namely, there is a possibility of theaxial position of the first lens group supporting frame 32 deviatingfrom the correct position thereof due to rotation thereof which can becaused by friction since the first lens group supporting frame 32 iscoupled to the first lens group moving frame 29 via the threadengagement of the male thread portion of the first lens group supportingframe 32 with the female thread portion 29 d of the inner flange 29 g ofthe first lens group moving frame 29. Nevertheless, in the presentembodiment of the zoom lens barrel, such friction is not produced evenif the first and second lens group moving frames 29 and 31 rotaterelative to each other at their respective accommodation positionsbecause the low-frictional ring sheet 38 is fixed to the front surfaceof the shutter pressure plate 37.

The overall movement of the zoom lens barrel 10, having the abovedescribed structure, from the accommodation position to a photographingposition (a position in the zooming section) will be hereinafterdiscussed.

When the zoom lens barrel 10 is in an accommodation position, the firstlens group supporting frame 32 which is supported by the first lensgroup moving frame 29, which is biased rearward by the three helicalcompression springs 30, is retracted to the above described mechanicallycontacting point P, where the lens pressure ring 32 a comes in contactwith the low-frictional ring sheet 38 due to the clearance between thefirst-lens-group accommodation portion C1A1 and the associated followerpin 29 f of the first lens group moving frame 29. The second lens groupmoving frame 31 is also retracted to the above described mechanicallycontacting point Q, where the second lens group moving frame 31 comes incontact with the third lens frame 39 due to the clearance between thesecond-lens-group-accommodation end portion C1S2 and the associatedfollower pin 31 f of the second lens group moving frame 31. Furthermore,the third lens frame 39 is retracted to the above described mechanicallycontacting point R, where the third lens frame 39 comes in contactagainst the spring force of the helical compression spring 42 with thehelical compression spring 42 being in a compressed (contracted) state.With these three mechanical contacts at the mechanically contactingpoints P, Q and R, the length of the zoom lens barrel 10 in anaccommodation position is successfully reduced. When the zoom lensbarrel 10 is in an accommodation position, the pair of barrier blades 46are closed to shut the photographing aperture 45 a, since the threerotation transfer faces 22 d respectively press the three engagingportions 44 a of the barrier drive ring 44 against the spring force ofthe helical extension spring 49 to rotate the barrier drive ring 44 in adirection to move the two drive projections 44 c away from the twoengaging projections 46 a of the pair of barrier blades 46,respectively.

In the accommodation position of the zoom lens barrel 10, when therotational ring 20 rotates in a direction to extend the zoom lens barrel10 relative to the stationary barrel 11, the cam ring 22, which isprovided with the three follower pins 22 f, and the biasing ring 21,which is provided with the three follower pins 21 f, rotate about theoptical axis O in accordance with the cam profile of the accommodationgroove portion 11 a 2 of each of the three cam grooves 11 a that areformed on an inner peripheral surface of the stationary barrel 11 (seeFIG. 28). This rotational movement of the cam ring 22 causes eachfollower pin 29 f and the associated follower pin 31 f, which arerespectively engaged in the first-lens-group accommodation portion C1A1of the associated lens-drive cam groove C1 and thesecond-lens-group-accommodation end portion C1S2 of the same lens-drivecam groove C1, to vary the relative position between the follower pin 29f and the follower pins 31 f in a circumferential direction of the camring 22 without varying the position of each of the follower pin 29 fand the follower pins 31 f relative to the cam ring 22 in the opticalaxis direction (see the transition from (a) to (b) in FIG. 23).Thereafter, each follower pin 21 f of the biasing ring 21 and eachfollower pin 22 f of the cam ring 22 enter the position-changing grooveportion 11 a 3, so that the cam ring 22 together with the biasing ring21 moves forward in the optical axis direction while rotating about theoptical axis O. This causes the second lens group moving frame 31 todisengage from the third lens frame 39, and almost at the same time,each follower pin 29 f of the first lens group moving frame 29 startsmoving rearward in the optical axis direction with respect to the camring 22 (see (b) in FIG. 23). As a result, the first lens group movingframe 29 presses the second lens group moving frame 31 rearward in theoptical axis direction to move the second lens group moving frame 31slightly in the rearward direction. The displacement of the second lensgroup moving frame 31 at this time is very small, and thus is not shownin FIG. 23. In an early stage of this rotation of the cam ring 22 by theposition-changing groove portions 11 a 3 of the stationary barrel 11,the three rotation transfer faces 22 d of the cam ring 22 arerespectively disengaged from the three engaging portions 44 a of thebarrier drive ring 44 so that the barrier drive ring 44 is rotated in adirection to open the pair of barrier blades 45 by the spring force ofthe helical extension spring 49 against the spring force of the twotorsion springs 47. Meanwhile, the second lens group moving frame 31rotates about the optical axis O relative to the first lens group movingframe 29 so that the lens pressure ring 32 a fixed to the first lensgroup supporting frame 32 rotatably slides on the low-frictional ringsheet 38 before and after the opening operation of the pair of barrierblades 46.

Subsequently, further forward movement of each follower pin 21 f of thebiasing ring 21 and each follower pin 22 f of the cam ring 22 in theposition-changing groove portion 11 a 3 (see FIG. 28) causes the secondlens group moving frame 31 to start moving rearward in the optical axisdirection (see (c) in FIG. 23). Thereafter, the first and second lensgroup moving frames 29 and 31 move rearward in the optical axisdirection with respect to the cam ring 22 as shown in FIG. 23 (see (c)and (d) in FIG. 23). Subsequently, the mechanical contact between thefirst and second lens group moving frames 29 and 31 is released at thetime the first lens group moving frame 29 moves forward in the opticalaxis direction (see (d) and (e) in FIG. 23). Subsequently, themechanical contact between the second lens group moving frame 31 and thethird lens frame 39 is released, and thereafter each of the three linearguide keys 31 a is engaged in the associated one of the four linearguide grooves 29 c (see (f) in FIG. 23).

Thereafter, the first and second lens group moving frames 29 and 31 moveto the respective wide-angle extremities thereof in the optical axisdirection while maintaining the circumferential space therebetween untileach follower pin 21 f and each follower pin 22 f reach the respectivewide-angle extremities thereof in the zooming groove portion 11 a 4 ofthe associated one of the three cam grooves 11 a that are formed on theinner peripheral surface of the stationary barrel 11 (see FIGS. 21Fthrough 21J).

Further rotation of the rotational ring 20 causes each follower pin 21 fof the biasing ring 21 and each follower pin 22 f of the cam ring 22 tomove from the respective wide-angle extremities in the zooming grooveportion 11 a 4 toward the respective telephoto extremities, so that thecam ring 22 rotates about the optical axis O without moving in theoptical axis direction. At this stage, if the cam ring 22 rotates in thezooming range (i.e., if each follower pin 29 f and each follower pin 31f move in the first-lens-group zooming section C1Z1 and thesecond-lens-group zooming section C1Z2, respectively), the first andsecond lens group moving frames 29 and 31 (the first and second lensgroups L1 and L2) move in the optical axis direction in accordance withthe cam profiles of the first-lens-group zooming section C1Z1 and thesecond-lens-group zooming section C1Z2, to thereby vary the focal lengthof the photographing optical system, i.e., to perform a zoomingoperation. This zooming operation is carried out by manually operating aconventional zoom switch or knob (not shown). Immediately after arelease button is depressed, the aforementioned step motor (not shown),which drives the feed screw shaft 41 to move the third lens group L3(the third lens frame 39), rotates by an amount of rotationcorresponding to information on a photographing distance to move thethird lens group L3 to bring an object into focus. The shutter unit 36drives the shutter blades 36 a (see FIGS. 8, 9 or 10) to open and closein accordance with the information on the object brightness.

Backlash and play between the three follower pins 21 f of the biasingring 21, the three follower pins 22 f of the cam ring 22 and the zoominggroove portions 11 a 4 of the three cam grooves 11 a of the stationarybarrel 11 are removed at the time the motor 18 stops during the timeeach of the three follower pins 21 f and the associated one of the threefollower pins 22 f are moving in the zooming groove portion 11 a 4 ofthe associated one of the three cam grooves 11 a, since each followerpin 21 f of the biasing ring 21 and the associated one of the threefollower pins 22 f of the cam ring 22 are pressed against a rear sideedge of the associated cam groove 11 a and a front side edge of the samecam groove 11 a, respectively, over the full range of the cam groove 11a by the spring force of the three compression helical springs 26 asdescribed above.

When the first lens group moving frame 29 moves linearly in the opticalaxis direction, the first ring 28 also moves in the optical axisdirection without varying the position thereof relative to the firstlens group moving frame 29 due to the engagement of the three followerpins 28 f with the three cam grooves C2 of the cam ring 22, the profilesof which are similar to those of the lens-drive cam grooves C1. At thesame time, the first ring 28 and the second ring 27, the respectiveouter peripheral surfaces of which are exposed to the outside of thezoom lens barrel 10, move together in the optical axis direction sincethe second ring 27 moves together with the cam ring 22 in the opticalaxis direction at all times due to the engagement of the three bayonetprongs 27 c of the second ring 27 with the three bayonet prongs 24 ofthe cam ring 22.

On the other hand, when the cam ring 22 rotates in a direction from thezooming section via the preparation section (i.e., in the barrierclosing direction), the first and second rings 28 and 27 retracttogether in the optical axis direction by operations reverse to theabove described operations. Subsequently, the first lens group movingframe 29, which supports the first lens group L1, and the second lensgroup moving frame 31, which supports the second lens group L2, comeinto contact with each other at their respective rear ends via the threehelical compression springs 30. Subsequently, the second lens groupmoving frame 31 retreats until coming into contact with the third lensframe 39. Subsequently, the second lens group moving frame 31 furtherretreats until the third lens frame 39 comes into contact with the CCDholding frame 13 against the spring force of the helical compressionspring 42, which biases the third lens frame 39 forward. At the sametime, the three rotation transfer faces 22 d respectively press thethree engaging portions 44 a of the barrier drive ring 44 against thespring force of the helical extension spring 49 to rotate the barrierdrive ring 44 in a direction to close the pair of barrier blades 46 toshut the photographing aperture 45 a.

In the above illustrated embodiment of the zoom lens barrel, the camring (lens support ring) 22 moves in the optical axis direction whilerotating about the optical axis O in a range between the accommodationposition and the wide-angle extremity, and only rotates about theoptical axis without moving in the optical axis direction in a zoomingrange between the wide-angle extremity and the telephoto extremity. Thisoperation of the cam ring 22 is achieved by the three follower pins(first cam followers) 22 f, which are formed on an outer peripheralsurface of the cam ring 22 at the rear end thereof, and the three camgrooves 11 a, which are formed on an inner peripheral surface of theouter cylindrical portion 11 b of the stationary barrel 11 and in whichthe three follower pins 22 f are respectively engaged. As has beendescribed above, backlash and play between the three follower pins 22 fand the three cam grooves 11 a are removed with the biasing ring 21 andthe three compression helical springs 26. This mechanism for removingsuch backlash and play will be hereinafter discussed in detail.

In the present embodiment of the zoom lens barrel, the three followerpins (second cam followers) 21 f of the biasing ring 21 are respectivelyengaged in the three cam grooves 11 a, in which the three follower pins22 f are respectively engaged. Furthermore, each follower pin 21 f ofthe biasing ring 21 and each follower pin 22 f of the cam ring 22 arepressed against a rear side edge (guide surface/rear guide surface) RSof the associated cam groove 11 a and a front side edge (guidesurface/front guide surface) FS of the same cam groove 11 a,respectively (see FIGS. 28 and 29). This structure simplifies andminiaturizes of the mechanism for removing backlash and play between thethree follower pins 22 f and the set of three cam grooves 11 a. Sincethe zooming groove portion 11 a 4 of each cam groove 11 a is formed toextend only in a circumferential direction of the cam ring 22(perpendicular to the optical axis) as described above, the spring forceof the three compression helical springs 26 is necessary to stabilizethe axial position of each follower pin 22 f in the zooming grooveportion 11 a 4 of the associated cam groove 11 a. Therefore, the zoomlens barrel 10 needs to be provided therein with a reaction forcereceiving portion(s) which receive the reaction force of the threecompression helical springs 26. As shown in FIG. 29, in the presentembodiment of the zoom lens barrel, such a reaction force is transferredto the biasing ring 21 via the three compression helical springs 26, andis subsequently transferred to the rear side edges RS of the three camgrooves 11 a via the set of three follower pins 21 f, respectively. Inother words, the three cam grooves 11 a themselves serve as the reactionforce receiving portions that receive the reaction force of the threecompression helical springs 26. This eliminates the necessity forproviding any additional elements serving as the reaction forcereceiving portion(s), thus simplifying the structure of the zoom lensbarrel 10.

The outer diameter of the biasing ring 21 is small, substantially thesame size as the outer diameter of the cam ring 22; furthermore, thethickness of the biasing ring 21 is also small. Accordingly, the biasingring 21 does not consume much space in the zoom lens barrel 10.

Since the three cam grooves 11 a serve as the reaction force receivingportions that receive the reaction force exerted on the biasing ring 21,the biasing ring 21 that is small enough so as to be able to be anintegral part of the cam ring 22 can be adopted. The biasing ring 21 andthe cam ring 22 are connected to each other by fitting respective baseportions of the three follower pins 22 f of the cam ring 22 in the threerecesses 21 b of the biasing ring 21, respectively. This connectingstructure is small and simple.

In the present embodiment of the zoom lens barrel, each follower pin 22f of the cam ring 22 is pressed against the front side edge (the sideedge on the object side) FS of the associated cam groove 11 a to beguided along the front side edge FS thereon, while each follower pin 21f of the biasing ring 21 is pressed against the rear side edge (the sideedge on the side of an image plane) RS of the associated cam groove 11 ato be guided along the rear side edge RS thereon. An impact (externalforce) applied to a lens barrel in the optical axis direction is oftentransferred from the front end to the rear end of the lens barrel, i.e.,from the object side to the image plane side. In this case, in the threecam grooves 11 a and in the vicinity thereof, the impact is received bythe rear side edges RS of the three cam grooves 11 a via the threefollower pins 21 f, respectively. As a result, a portion on the rearside edge RS of each cam groove 11 a against which the associatedfollower pin 21 f bumps hard may be slightly dented. However, even ifthe rear side edge RS is dented, this has no effect on the precision inpositioning the cam ring 22 in the optical axis direction since the rearside edge RS of each cam groove 11 a does not directly guide the camring 22 (namely, the front side edge FS of each cam groove 11 a directlyguides the cam ring 22). The axial position of the cam ring 22 on theoptical axis O is more important than that of the biasing ring 21 sincethe cam ring 22 supports lens groups (the first and second lens groupsL1 and L2) therein. Unlike the present embodiment, if the three followerpins 22 f are pressed against the rear side edges RS of the three camgrooves 11 a to be guided along the rear side edges RS thereon,respectively, and if a portion on the rear side edge RS against whichthe associated follower pin 22 f bumps hard is dented, the dentedportion would have a substantial and undesirable effect on the precisionin positioning the cam ring 22 in the optical axis direction, i.e., inpositioning the first and second lens groups L1 and L2. Unlike thisstructure, i.e., according to the present embodiment of the zoom lensbarrel 10, no substantial problems occur even if the rear side edge RSis slightly dented as long as the rear side edge RS serves as thereaction force receiving portion.

As can be seen in FIGS. 28 and 29, the width of each cam groove 11 a onthe stationary barrel 11 is greater than the diameter of either followerpin 21 f or 22 f so that none of the follower pins 21 f and 22 f contactthe front side edge FS and the rear side edge RS of the associated camgroove 11 a at the same time. Due to this structure, there is littlepossibility of the front side edge FS or the rear side edge RS beingdented by an impact exerted thereon by the associated follower pin 21 for 22 f if bumped towards either side edge FS or RS due to an externalimpact on the zoom lens barrel 10.

As can be seen from FIG. 29, a mutual distance D1 in the optical axisdirection between the axis of each follower pin 22 f of the cam ring 22and the axis of the associated follower pin 21 f of the biasing ring 21when the follower pins 22 f and 21 f are engaged in theposition-changing groove portion 11 a 3, is slightly greater than amutual distance D2 in the optical axis direction between the axis ofeach follower pin 22 f of the cam ring 22 and the axis of the associatedfollower pin 21 f of the biasing ring 21 when the follower pins 22 f and21 f are engaged in the zooming groove portion 11 a 4 in the opticalaxis direction. Due to this structure, a constant and sufficient biasingforce for removing backlash and play between the three follower pins 22f and the three cam grooves 11 a is exerted on the rear side edges RS ofthe three cam grooves 11 a via the three follower pins 21 f,respectively, by the three compression helical springs 26 when eachfollower pin 22 f is in the zooming groove portion 11 a 4, whereas sucha biasing force for removing backlash and play between the threefollower pins 22 f and the three cam grooves 11 a decreases when eachfollower pin 22 f is in the position-changing groove portion 11 a 3since each of the three compression helical spring 26 slightly expandsto reduce the biasing force exerted on the three follower pins 21 f andthe three follower pins 22 f when each follower pin 22 f is in theposition-changing groove portion 11 a 3.

Namely, when the follower pins 21 f and 22 f are positioned in theposition-changing groove portion 11 a 3, since the slide-friction(resistance) which occurs between each follower pins 21 f, 22 f and theassociated cam groove 11 a is reduced, the load on a zoom lens drivesystem of the zoom lens barrel 10, which includes the motor 18, islightened.

This effect is achieved by an arrangement of the three follower pins 21f and the three follower pins 22 f which are engaged in the three camgrooves 11 a of the stationary barrel 11 at different circumferentialpositions, respectively, to correspond to the shape (inclination) of theposition-changing groove portion 11 a 3. In other words, the respectivepositions of each follower pin 21 f and the associated follower pin 22f, which are engaged in the common cam groove 11 a, are constant in theoptical axis direction as long as these follower pins 21 f and 22 f areengaged in the zooming groove portion 11 a 4. On the other hand, theposition-changing groove portion 11 a 3 extends in a direction inclinedwith respect to both the optical axis O and a circumferential directionof the cam ring 22 to gradually approach the front side of the cam ring22 with respect to the optical axis O in a direction from theaccommodation groove portion 11 a 2 to the zooming groove portion 11 a4. Therefore, if each follower pin 21 f and the associated follower pin22 f are arranged in the associated cam groove 11 a in a positionalrelationship such as shown in FIGS. 28 and 29 (i.e., in a positionalrelationship wherein each follower pin 22 f biased in a forwarddirection in the position-changing groove portion 11 a 3 is arrangedcloser to the zooming groove portion 11 a 4 of the associated cam groove11 a, while each follower pin 21 f biased in a rearward direction in theposition-changing groove portion 11 a 3 is arranged closer to theaccommodation groove portion 11 a 2 of the associated cam groove 11 a),the mutual distance D1 between the axis of each follower pin 22 f andthe axis of the associated follower pin 21 f when the follower pins 22 fand 21 f are engaged in the position-changing groove portion 11 a 3becomes slightly greater than the mutual distance D2 between the axis ofeach follower pin 22 f and the axis of the associated follower pin 21 fwhen the follower pins 22 f and 21 f are engaged in the zooming grooveportion 11 a 4 in the optical axis direction by an amount correspondingto the amount of inclination of the position-changing groove portion 11a 3 with respect to both the optical axis O and a circumferentialdirection of the cam ring 22.

In the present embodiment of the zoom lens barrel, the threerotation-transmission arms 20 b of the rotational ring 20 that are usedto rotate the cam ring 22 are respectively engaged in the three recesses21 a of the biasing ring 21 so as not to rotate about the optical axis Orelative to the three recesses 21 a (so as to be slidably movable in thethree recesses 21 a in the optical axis direction relative to the threerecesses 21 a). Accordingly, it can be said that the cam ring 22 and thebiasing ring 21 are coupled to each other via the rotational ring 20.Hence, the coupling between the cam ring 22 and the biasing ring 21,which rotate as an integral unit when they rotate, has excellentstrength.

The present invention is not limited solely to the above describedparticular embodiment. For instance, although the present invention isapplied to the guide mechanism using cam grooves which is providedbetween the cam ring 22 and the stationary barrel 11 in the aboveillustrated embodiment, the present invention can also be applied toanother guide mechanism using cam grooves which is provided between alens support member, which supports a lens group more directly such asthe first lens group moving frame 29 or the second lens group movingframe 31, and the cam ring 22.

Regarding relationships among rotational and non-rotational members ofthe zoom lens barrel 10, although the cam ring 22 having a set of camfollowers (22 f) is a rotatable member while the stationary barrel 11having a corresponding set of cam grooves (11 a) is a non-rotatablemember in the above illustrated embodiment of the zoom lens barrel, thepresent invention can also be applied to the case where a member (e.g.,the first lens group moving frame 29 or the second lens group movingframe 31) having a set of cam followers is a linearly guided memberwhich is guided in the optical axis direction without rotating about theoptical axis O while another member (e.g., the cam ring 22) having acorresponding set of cam grooves on an inner peripheral surface thereofis a rotatable member.

The present invention can be applied not only to the above describedparticular type of lens barrel, but also to other types of lens barrels.

As can be understood from the above description, a lens barrel isachieved which incorporates a guide mechanism using a cam groove(s) anda cam follower(s) which is engaged in the cam groove, wherein backlashand play between the cam groove and the cam follower is reliably removedvia a simple and small mechanism.

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

What is claimed is:
 1. A lens barrel comprising: a ring member having acam groove formed on an inner peripheral surface thereof, said camgroove including opposite guide surfaces; a lens support ring positionedin said ring member and supported thereby to be rotatable with respectto said ring member, said lens support ring having a first cam followerwhich is engaged in said cam groove of said ring member; a biasing ringcoupled to said lens support ring to be movable in an optical axisdirection and to be non-rotatable about said optical axis with respectto said lens support ring, said biasing ring having a second camfollower which is engaged in said cam groove of said ring member; and abiasing device for biasing said lens support ring and said biasing ringin opposite directions in said optical axis direction to press saidfirst cam follower and said second cam follower against said oppositeguide surfaces of said cam groove.
 2. The lens barrel according to claim1, said biasing device biases said lens support ring and said biasingring in opposite directions away from each other in said optical axisdirection.
 3. The lens barrel according to claim 1, wherein saidopposite guide surfaces of said cam groove comprise a front guidesurface and a rear guide surface, said front guide surface beingprovided at a forward position of said optical axis and said rear guidesurface being provided at a rearward position of said optical axis;wherein said first cam follower is pressed against said front guidesurface and said second cam follower is pressed against said rear guidesurface.
 4. The lens barrel according to claim 1, wherein said first camfollower is formed on an outer peripheral surface of said lens supportring, at a rear end thereof in said optical axis direction; wherein aradial end portion of said first cam follower is engaged in said camgroove; and wherein a base portion of said first cam follower is fittedin a recess formed on said biasing ring.
 5. The lens barrel according toclaim 1, wherein said first cam follower and said second cam followerare pressed against one of said opposite guide surfaces and the other ofsaid opposite guide surfaces, respectively, with said first cam followerand said second cam follower not being in contact with said other ofsaid opposite guide surfaces and said one of said opposite guidesurfaces, respectively.
 6. The lens barrel according to claim 1, whereina mutual distance in said optical axis direction between said first camfollower and said second cam follower changes in accordance withmovement of said first and second cam followers along said cam groove.7. The lens barrel according to claim 6, wherein said lens barrelcomprises a zoom lens barrel; wherein said cam groove includes a zoominggroove portion used to change a position of said zoom lens barrelbetween a telephoto extremity and a wide-angle extremity; and aphotographing preparation groove portion which extends from one end ofsaid zooming groove portion to an accommodation position; and whereinsaid mutual distance between said first and second cam followers whensaid first and second cam followers are engaged in saidphotographing-preparation groove portion is greater than when said firstand second cam followers are engaged in said zooming groove portion. 8.The lens barrel according to claim 7, wherein said zooming grooveportion extends only in a circumferential direction of said lens supportring, perpendicular to the optical axis; wherein saidphotographing-preparation groove portion extends in a direction inclinedwith respect to both said optical axis and said circumferentialdirection of said lens support ring; and wherein said first cam followerand said second cam follower are engaged in said cam groove at differentcircumferential positions of said lens support ring.
 9. The lens barrelaccording to claim 1, wherein said ring member a stationary barrel fixedto a camera body, said lens barrel further comprising a rotationtransfer ring via which a rotational motion is transferred to said lenssupport ring, said rotation transfer ring being supported by said ringmember so as to be immovable in said optical axis direction and to berotatable about said optical axis with respect to said ring member. 10.The lens barrel according to claim 9, wherein said rotation transferring is engaged with said lens support ring and said biasing ring to benon-rotatable with respect to both said lens support ring and saidbiasing ring.
 11. The lens barrel according to claim 9, wherein saidbiasing device comprises at least one compression spring providedbetween said lens support ring and said biasing ring.
 12. The lensbarrel according to claim 9, further comprising a motor which generatessaid rotational motion, so that said rotation transfer ring transferssaid rotational motion from said motor to said lens support ring. 13.The lens barrel according to claim 1, wherein said lens support ringcomprises a plurality of first cam grooves and a plurality of second camgrooves which are formed on an inner peripheral surface of said lenssupport ring and an outer peripheral surface of said lens support ring,respectively.